1. Technical Field
The present disclosure relates to a metropolitan wide area network for telecommunication systems. In particular, this invention relates to the integration of a wireless point to multi point system operating in the millimeter microwave radio range with an intelligent metropolitan area broadband backbone network to enable a variety of enhanced voice, broadband data and multimedia telecommunication services.
2. Description of Related Art
In the art, point-to-point narrow band, point to multi point narrow band and point to point broadband fixed wireless systems are generally known. Point to multi point radio technology is also a known technology which has been generally used for narrowband communications, such as voice. Narrow band systems are typically systems that are capable of generating at or below 1.544 megabits per second of data in a single circuit or channel, whereas broadband systems are capable of generating data rates above 1.544 megabits per seconds per circuit or channel. While narrowband xe2x80x9cpoint to multi pointxe2x80x9d systems have been used for voice communications, point to multi point systems have not been generally applied to broadband telecommunications networks.
Today""s narrowband point to multi point systems can aggregate a group of up to twenty four 64 kilobits per second channels together in what is called a xe2x80x9cT1 line.xe2x80x9d However, this T1 line is still considered a narrowband facility when it is used to support multiple voice channels. Narrowband point to multi point systems have also been in use in Europe for voice telephone networks for several years.
Point-to-point broadband technology is also well known. Above 18 Gigahertz (millimeter microwave frequencies), and especially in the 37 Gigahertz or xe2x80x9cGHzxe2x80x9d to 40 GHz range (typically referred to as xe2x80x9c38 GHzxe2x80x9d), point-to-point broadband wireless systems are in use. When such broadband wireless links are engineered properly, their performance is functionally equivalent to that of fiber optic telecommunications.
Fixed wireless technology at frequencies of 18 GHz and above is gaining popularity as means for transmission of telecommunication services because of its low cost, rapid installation and ease of operation. Connecting two sites with point-to-point wireless service largely consists of installing roof top antennas on the top of two buildings, with the accompanying indoor equipment. Physical wires do not have to be connected between the buildings, representing a significant advantage over copper or fiber technology. Bringing fiber or copper to buildings entails tremendous labor and other costs associated with digging up streets, obtaining permits, etc. Because the deployment of broadband fixed wireless systems does not require civil construction in most instances, it is thus faster and more economical to install than traditional methods of xe2x80x9clast milexe2x80x9d interconnection in metropolitan area telecommunications networks.
Current fixed wireless technology operating at frequencies of 18 GHZ and above (millimeter microwave wave) has a number of characteristics that make it an attractive commercial telecommunications transport medium. Fixed millimeter microwave wireless technology provides a high bandwidth path for voice, data, multimedia and video. Current technology permits link distances of up to five miles. Since all millimeter microwave propagation is subject to rainfall degradation, actual distance is a function of geographical location or xe2x80x9crain region.xe2x80x9d In climates where heavy rainfall is common, shorter link distances may be required to achieve performance and availability equivalent to that of fiber.
Millimeter microwave radio propagation generally requires unobstructed line-of-sight transmission. In practice, small diameter antennas are mounted on office building rooftops, and in some cases in office building windows. The size of the antennas vary according to the selected frequency band, but typically range from 12 to 24 inches in diameter. Manufacturers indicate mean time between failure (MTBF) statistics in excess of 10 years for the radio and modem components, indicating that the hardware is highly reliable. Current fixed wireless millimeter microwave technology is therefore ideally suited for high availability broadband point-to-point commercial voice and data applications ranging from 1.544 Megabits per second (T1) to 45 Megabits per second (DS3) capacities.
One example of a typical wireless point-to-point broadband commercial application is the interconnection of multiple servers in a campus local area network (LAN). Another such application is metropolitan wide area networking. Here multiple campus LANs within the same city are interconnected via wireless facilities operations at millimeter wave frequencies. Dedicated access to inter-exchange carriers (IXCs), Internet Service Providers (ISPs) and other alternate access arrangements are common point-to-point business applications for millimeter wave wireless links. For example, cellular and personal communication services (PCS) operators may deploy high availability wireless facilities in a millimeter microwave range in their backbone networks to support back haul between antenna sites, base stations and mobile telephone switching offices (MTSO""s). Wireless point-to-point millimeter microwave technology is also being used to provide mission critical protection channels and other point-to-point alternate routing where extension is required from a fiber network to a location that is not served by fiber. Finally, interconnection with the public switched telephone network (PSTN) for the provision of local dial tone by competitive local exchange carriers (CLECs) utilizing point-to-point millimeter microwave wireless technology is becoming increasingly popular.
FIG. 2 illustrates a basic point-to-point wireless facility providing customer interconnection to services. This connection will support broadband (data, video etc.) and narrowband (voice) applications. A customer building is shown as 200 and may contain multiple tenants. It is connected to another building 202 that houses a telecommunications network switch 203. These buildings are connected by a wireless link between two roof top antennas: one antenna 204 at the customer building, the other antenna 205 at the building housing the switch 203. The bandwidth of this connection could be up to 28 T1 circuits, or DS3 (45 Megabits per second). The switch 203 connects to the PSTN 206, or public switched telephone network for local service, and to long distance networks 207 for long distance service. The switch 203 is also able to provide dial up access to the Internet 208.
FIG. 3 is a representation of an exemplary system defined channelized spectrum allocation plan suitable for use in millimeter microwave frequencies. For example, the FCC spectrum allocation plan for an exemplary millimeter microwave band at about 38 GHz consists of 14 total channels. Each channel is 100 MegaHertz (MHZ) in bandwidth. Each 100 MHZ channel consist of two 50 MHZ sub channels, one sub channel to transmit and the other sub channel to receive. These two 50 MHZ sub channels are separated by 700 MHZ of spectrum. As shown in FIG. 3, sub channel 1A is 50 MHZ wide and it is a transmitting channel, whereas sub channel 1B is 50 MHZ wide and it is a receiving channel. Sub channel 1A is separated from sub channel 1B by 700 MHz. This band plan yields 14 channels (1400 MHZ or 1.4 GHz) of spectrum in the FCC allocated 38 to 40 GHz range. Similar frequency channel allocations can be established (and planned) in other millimeter microwave frequencies as well, including 24, 28 and 40 GHz in the United States and 23 and 26 GHz in Europe. For example, in the 28 GHz LMDS band (in the United States) spectrum is largely allocated in a single 850 MHZ wide spectral block. However, such a block spectrum allocation can be subdivided into system defined channels, to achieve the same result to that shown in FIG. 3.
Referring to FIG. 4, a basic spectrum management problem associated with the use of point-to-point wireless systems in a metropolitan area using a channelized spectrum allocation as illustrated in FIG. 3 is shown. Because buildings are close to each other in a metropolitan area, the broadcast of information over wireless links may overlap, making the use of the same channel (1A/1B) in contiguous systems impossible. In this figure, one antenna from one building is transmitting its signal to the antenna of the intended receiver, but a portion of the signal is also being received by the antenna on the adjacent building. Such signal corruption is termed xe2x80x9cco-channel interference.xe2x80x9d
In FIG. 4, a host building 401 containing a switch 402 is connected via four rooftop antennas 403A, 403B, 403C and 403D respectively to remote buildings 404A, 404B, 404C and 404D, each with its own corresponding rooftop antenna. Shown between these buildings is a conceptual representation of the spectrum being utilized by each of these point-to-point wireless systems. As buildings get close together, transmission signals between buildings begin to overlap. To prevent the co-channel interference described in the preceding paragraph, different channels must be used to connect buildings that are in close proximity. For instance, channel 1A/1B is used for building 404D and channel 2A/2B is used for building 404C. Even though channel 1A/1B partially overlaps the transmission of 2A/2B, the use of different frequencies (channels) by the two systems provides protection from co-channel interference. Thus the antenna of one building may be transmitting a portion of its signal to the wrong receiving antenna, but each system is xe2x80x9ctunedxe2x80x9d to a different frequency and transmission from neighboring systems using other frequencies is ignored.
The frequency management technique shown in FIG. 4 avoids co-channel interference in wireless networks deployed in dense urban areas, however the use of additional channels to avoid co-channel interference does not maximize the information transport capacity of the licensed spectrum and is therefore inefficient. A solution to this problem is needed.
FIG. 5 illustrates an additional spectrum management problem associated with point-to-point systems. Building 501 connects to Building 502 through channel 1. Building 503 connects to building 504 through channel 2. The solid connection lines 505, 506 represent the wireless transmission that is intended. However, because the xe2x80x9ctransmit beamxe2x80x9d is about 2 degrees at the source, signals can be received by other systems that are not planned but happen to be in the range of the transmit beam of the originating system. The dotted line 507 represents such a case, where the system in building 4 incorrectly receives the transmission of the system in building 1. If two distinct frequencies were used, there would be no co-channel interference. Once again, frequency management in point-to-point wireless networks requires the use of multiple channels to avoid interference rather than allowing the spectrum to be used to drive incremental bandwidth.
Rooftop space is expensive and in many cases there are restrictions on the number, size and position of antennas deployed on a roof. Because point-to-point systems use separate antennas for each wireless connection, space becomes a limiting factor on building rooftops. As the number of point-to-point systems located on a building increases, not only do spectrum management considerations limit the number of systems which can be deployed, but the physical space available for each antenna on the roof also constrains the number of systems. Thus, a solution is required which permits the expansion of wireless network capacity, and thus the number of users, without a corresponding increase in the number of antennas rooftops.
Point-to-point systems provide users with what is called a full period connection. Full period connections are xe2x80x9calways onxe2x80x9d (connected and active), awaiting the transport of information. Full period wireless connections utilize dedicated spectrum which, once assigned, is unavailable to other users. Point-to-point wireless systems are therefore appropriate for applications involving continuous or lengthy transmissions. Point-to-point systems do not efficiently support variable bit rate or xe2x80x9cburstyxe2x80x9d data services where the requirement for bandwidth is not constant but rather variable. Bandwidth utilized by point-to-point systems for variable bit rate applications is wasted, as each system utilizes the allocated channel on a full time xe2x80x9calways onxe2x80x9d basis regardless of the amount of information or the duration of transmissions on the link. A solution is required to more efficiently utilize spectrum for xe2x80x9cburstyxe2x80x9d data services like LAN to LAN data transmission.
It is an object to create a xe2x80x9cfull featuredxe2x80x9d local metropolitan area broadband telecommunications network infrastructure capable of supporting advanced voice and data services.
It is another object to use fixed wireless telecommunications technology as a key enabler of broadband local access to a metropolitan area telecommunications network offering advanced voice and data services.
It is an object to maximize the utilization of allocated spectrum available in local metropolitan area broadband telecommunications networks.
It is an object to overcome the spectrum management limitations associated with the use of point-to-point fixed wireless telecommunications systems.
It is an object to allow the utilization of multiple channels to drive additional network capacity in local metropolitan area broadband telecommunications networks.
It is an object to minimize the number of wireless telecommunication systems required on rooftops to provide access to local metropolitan area broadband telecommunications networks.
In accordance with one form of the present network, a wide area communication network includes at least two hub sites which are interconnected by a communication backbone Each hub site provides wireless coverage in at least one sector. At least two remote sites reside in each sectors and are coupled to a corresponding hub site via a point to multi point broadband wireless system. The network preferably includes at least one service node which is accessible to the remote sites via the hub sites and backbone.
In accordance with another form of the present network, a broadband local metropolitan area telecommunication network provides fixed broadband wireless local loop access to a plurality of subscribers. The subscribers include a subscriber radio unit operating on a millimeter microwave band frequency corresponding to a cell sector in which said subscriber resides. At least one of the subscribers has a plurality of associated customer premise equipment and includes means for performing statistical multiplexing among the plurality of customer premise equipment the subscriber radio unit. The network includes a plurality hub sites which are interconnected by a Sonet based back bone. The hub sites include a plurality of hub site radio units which operate on a selectable frequency with at least one radio unit corresponding to a cell sector. The hub sites further include means for dynamically allocating communication bandwidth among a plurality of subscribers within each said cell sector. The network preferably includes a plurality of value added service nodes which are coupled to the backbone and are accessible to subscribers through the hub sites and backbone. The network further includes a central operations node which is connected to each of said hub sites by a control network and provides remote access and control of the hub sites as well as remote control subscriber access to the value added service nodes.